1. Technical Field
This invention relates to auxiliary air filters useful in so-called clean air systems and negative air pressure systems incorporating HEPA filters in combination with air exhausting machines.
2. Description of Prior Art
U.S. Pat. No. 2,057,568 discloses a dust arrester comprising a pair of screened frames for positioning a filter element in a pipe communicating with a hot air furnace.
U.S. Pat. No. 4,549,887 discloses an electronic air filter in an enclosure provided with a hinged screen positioning air filter elements against another hinged screen.